Method and system for mobile station positioning in cellular communication networks

ABSTRACT

A system of cell phone positioning in real time is provided with specialized location device installations on multiplicity of base stations BSs in CDMA and TDMA cellular communication networks. The purpose of the positioning system is to enable tracking and locating large quantities of anonymous mobile cell phones MS in any number of network cells to be used for real time traffic-forecasting systems, emergency services E911, and other client-initiated position requests. Location data thus obtained can be continuously updated from vehicular-based cellular phones, collected, processed and used as a basis for input to intelligent transportation systems, such as real time urban traffic guidance for vehicular congestion and intelligent traffic control systems. The system is capable of covering large urban geographical areas and number of independent cell structures serving thousands of mobile cell phone clients. It is an independent plug-in solution with specialized synchronized location device installations in each cell BS. Centrally located specialized location software based on Time of Arrival (TOA) and Time Difference of Arrival (TDOA) methods for high speed location processing in central Location Database Server (LDS). The inventive system consists of number of component functions: Operator-initiated functions, location device functions and software enabled positioning functions.

FIELD OF THE INVENTION

[0001] This invention relates to tracking, positioning and determininglocations of plurality of mobile cell phones in wireless communicationnetworks such as CDMA, TDMA, AMPs, etc. More specifically, the inventionrelates to MS location methods in cellular communication networks.

BACKGROUND AND OBJECTS OF PRESENT INVENTION

[0002] Cellular Networks in USA comprises of 18,000 cell sites(statistics based on years 1998-99). Cell coverage varies for variouscellular systems and is overlapping. In many dense urban systems 7 to 8cell sites cover a geographic point, in less dense areas 3 to 4 siteshandle a call. The existing networks are therefore suited for ourlocation systems, which must receive transmitted signal from multiplesites. FCC 911 Public Safety Answering Point PSAP requires 125 m and 65%accuracy AMPS Cellular Networks serviced 28 million cell phones in USA1995 using AMPS standard “A” & “B” bands (416 channels, 30 kHz wide 21channels for control purposes and 395 voice purposes). These systems useReverse control channel—RACH for mobile phone locations (withtransmission of 10 Kbytes/sec where minimum time of one transmissionTx=100 ms). RACH generally can support 2 to 3 transmissions per second.Reverse control channel RACH is also used for various other functions:MS registration, call origination and call reception. All RACH Messagesare sent by conventional wire network to MTSO mobile switching office.CDMA and TDMA standard protocols conforming to AMPS are also widely usedin USA with some differences. GSM standard protocol is generally used inEurope and will not be generally considered for the inventive system.

[0003] Existing Location Technology and Methods such as SigmaOneLocation System, generally rely on the existing communication networks.Using independent system of data gathering equipment such as multipleLocation units and specialized Location Network Controller whichutilizes custom designed phase array antennas they attempt to providepositioning data with 150-250 meter accuracy.

[0004] These systems also use a number of known geometric methods tocalculate mobile cell phone coordinates: signal attenuation, angle ofarrival and time difference of arrival measurements. In the presentembodiment several improvements for precise positioning are proposed.

RELEVANT PATENT CASES

[0005] U.S. Pat. No. 5,890,069, “Wireless location System”. Proposesstrategy for TOA locations of mobile phones. All base stations BS aresynchronized by GPS-protocol (Global Positioning System).Super-Resolution (SR) mode measures time from all mobile MS to all basestations BS. Time is defined by compensations and by signal time delayat the input correlator, which is located after antenna array.Measurements are carried out in RECC mode (Reverse Control Channel)using 11-bits Barcker's code and 7-bits of signal sync code of frames.In this TOA method, mode delay line must consist of the generalsystem-feedback synchronizing both BTS and MS. It should be noted thatcompensation methods are slower than direct methods of measurements andless accurate. Locations of client MS are result of compensationmeasurements. No software application is presented for processing theresults of measurements.

[0006] U.S. Pat. No. 6,121,927, “Determination of Terminal Location inRadio System”. This patent proposes to use a pilot signal for locationmobile phones. Time of receipts of electromagnetic wave to antennas ofthree base stations BS is defined by the correlation processing ofsignals from array-antenna elements. In accepted standard levels,duration (time of correlations) is defined by mutual correlationfunctions. Direction and distance to MS is obtained by constructing 3circle-intersection, which defines the area of most likely MS location.This patent is proposed for IS-95 CDMA (Code Division Multiple Access)standard systems. As is well known, generally TOA techniques are lessaccurate in MS location calculations and no TDOA calculations areproposed in this patent.

[0007] U.S. Pat. No. 6,070,079, “Positioning Apparatus Used in CellularCommunication System and Capable of Carrying out a Positioning with aHigh Accuracy in Urban Area”. This patent proposes to define distance tothe mobile phone MS on the energy spectrum bandwidth of signal in theoutput correlator, which is located together with array antenna.Distance and direction to MS is defined by the power-gain bandwidth.Spread-spectrum processing in the correlator is processed by aprocessor. Use of the Fourier processor limits speed and accuracy ofmeasurement.

ADVANTAGES OF THE INVENTION

[0008] The present invention attempts to combine methods and tools fromseveral fields such as Intelligent Traffic Systems, cell phone emergencylocation services and intelligent computational applications. ITSsystems rely increasingly on smart signaling devices and sensors todetermine and map traffic congestion patterns in real time.

[0009] By obtaining multiplicity of MS coordinates simultaneously in alarge number of cell BSs, this invention provides real time data fortracking and mapping urban traffic congestion as proposed in U.S. patentapplication Ser. No. 09/528,134, “Real Time Vehicle Guidance andForecasting System Under Traffic Jam Conditions” (Makor Co.).

[0010] Cellular networks location systems can provide additionalcapabilities besides existing sensor device systems, for obtainingmoderately reliable position information and statistics for the TrafficService Center databases in ITS systems. While many previous patentsdescribed methods for individual MSs location in real time, none hasapplied MS positioning techniques to ITS systems.

[0011] The present invention also attempts to improve accuracy of manyproposed location devices. Using GPS-synchronized additional supportinglocation receivers in all monitoring BSs to calculate TDOA timedifference delay and ‘smart’ antennas with high gain RF coverage.

[0012] A comprehensive approach to position ambiguity will be used tosignificantly reduce position errors. The stand-by tracking positiondata will then be used on geographical road maps as a basis forcontinuous positioning.

[0013] Algorithmic methods include Attenuation, AOA and TDOA methods.

BRIEF DESCRIPTION OF THE INVENTION

[0014] The preferred embodiments of the invention deal with all relevantfunctions of System of Cell Phone Positioning in real time withspecialized Location Device installations on multiplicity of basestations BSs in CDMA an TDMA cellular communication networks. Thepurposed of the positioning system is to locate a large quantity ofanonymous mobile cell phones MS in any number of network cells to beused for real time traffic-forecasting systems, emergency services suchas E911, and other client-initiated position requests. The system iscapable of covering large urban geografical areas and number ofindependent cell structures serving thousands of mobile cell phoneclients. It is an independent turnkey solution with specializedsynchronized Location Device installations in each cell BS with acentrally located specialized triangulation software based on Angle ofArrival (AOA), Time of Arrival (TOA), and Time Difference of Arrival(TDOA) methods for high speed location processing. The inventive systemconsists of number of component functions: Operator-initiated functions,Location Device functions and software-controlled mathematicalfunctions.

[0015] Combination of location determining techniques AOA, TOA and TDOAwill be used for optimal location strategy. As the accuracy ofarray-antenna based direction determining AOA and TOA systems decreasesover the relative distance between base stations BS and mobile source MSthe TDOA hyperbolic/hyperboloid techniques complement and improve theoverall location performance. The TDOA location technique involves useof time delays of MS source signal between several base stations BSssynchronized receivers in CDMA standard. Results are calculated from aset of nonlinear equations and specialized algorithms are utilized tosolve problems of ambiguity. Two approaches are generally used in TDOA:subtracting TOA measurements from two BSs to produce relative TDOA, orusing cross-correlation techniques where received signal at one BS iscorrelated with the same signal at another BS.

[0016] Transmission timing is done with Global Positioning System GPSclock and full system synchronization is required between base stationsBSs and MS. In IS-95 CDMA standard full synchronization is available forrelative and cross-correlation TDOA techniques.

[0017] According to the present invention, a Location Device (LD)located in each BS will be used for signal correlation purposes as shownin FIG. 1a and FIG. 1b. It is based on the TDOA signal cross-correlationtechniques and will complement existing BS standard IS-95 CDMAequipment.

[0018] The LD's main purpose is to create a Timing Block (7) mechanismto efficiently correlate and quantify the arriving source signal fromtwo BS antennas A1 and A2. Two variations of Timing block mechanism areproposed here:

[0019] 1. LD consists of additional receiver (6 a) from supportingcommunication channel in antenna A2, specialized CDMA correlator (6)(see FIG. 1a) for compression of signal and special time intervalcounter for time delays in time block (7) in the time accumulation andtime interrupt mode. Resulting digital data is then transmitted viadigital interface to LDS database (4) for MS location calculations. TheLD is fully synchronized with the BS receiver (1) antenna A1 by thesystem GPS clock (5), PLL Synthesizer and Digital Clock (3) for digitalsignal processing. Group time of delay is measured by Timing Block (7)resulting from propagation delay due to spreading a from the MStransmitter (8) to the receiver (1). Time interval is measured betweenthe supporting signal from A2 synchronized in the PLL frequencysynthesizer (3) formed by the correlator (6) and by the receiver (1).Timing Block LD (7) measures sections of signal windows frames of timeintervals in CDMA to improve measurement accuracy. Time differencemeasurements of the signal delays come from two antennas A1 and A2 andthe time delay is measured between the signal from the receiver 1 andsignal from the correlator 6 in the additional supporting communicationchannel.

[0020] 2. For the simple time of arrival TOA technique a variation ofTiming Block (7) is proposed in FIG. 1a. A single existing Antenna A1 inBS receives mobile source signal and measures time delay between MSantenna A3. In this variation all BSs will be synchronized in thenetwork system clock such as exist in CDMA standard. Absolute timedifference measurements of MS signal are compared and calculated fromtwo different BSs. Time difference data for distance calculations arethen stored in the central LDS Location Register database.

[0021] The present invention proposes to use wireless 3D hyperbolictrilateral location method for determining cell phone position andfiltering out possible position ambiguities. Conventional radiolocationsystems locate a MS by measuring propagation times of the signalstraveling between the MS and a fixed set of BSs. There are three majortypes of radiolocation systems: those based on signal strength, orattenuation methods (AT), those based on angle of arrival (AOA), andthose measuring time of arrival (TOA or TDOA). After direction of pathsto/from a MS from/to multiple BSs have been determined, geometricalrelationships are used to determine the location. Each of the lines ofposition, i.e., the curves that describe the possible location of theMS, can be described mathematically using the relative geometry of theBSs and MS, while intersection of those lines indicates the presumedlocation of the MS. Locations of cell phones can be determined in thesame way. However, to achieve good accuracy in location estimates, it isnecessary that line of sight paths exist between the MS and the BSs thatare utilized in the location process. This cannot always be assumed inreal situations, especially in urban areas where ambiguities arisingfrom multiple crossings (multipath) are common. Therefore, variouscombinations of the above mentioned methods will be used for exhaustiveutilization the existing data on the one hand, and for filtering outpossible false locations on the other. The general scheme ofcomputations is shown in FIG. 7 and further details are given in theDetailed Description below.

[0022] The Cellular Network Operator-initiated Functions:

[0023] 1. Cellular network operator initiates a sequence of silentPositioning Request Signals (PRS) via BS control channel to mobilecellular phones MS's from the serving pilot BS according to somepredetermined order by mathematical algorithms. Since it is essential toobtain a large number of MS position signals, the operator must dealwith existing communication traffic constraints and the need forproviding continuous tracking of MS data.

[0024] 2. Mobile cellular phone MS responds to position signal PRS onlyif the MS is currently in stand-by (idle) mode in RACCH protocol. Theoperator can also obtain positioning data when MS is engaged however inthis discription we will concentrate on stand-by mode MS responses only.

[0025] 3. Location Device modules installed on serving BSs processsilent positioning response signals to co-located for Timing BlockTime-Start/Stop Stamping,TOA signal delays: τ₁, τ₂, . . . τ_(n), or TDOAΔτ for each MS.

[0026] 4. Operator maintains synchronization of cell base stationantennas via GPS system clock and in additional Location Device Antennas

[0027] 5. Receiving MS PRS signals from multiplicity of cell basestations equipped with LD modules

[0028] 6. Forwarding, from said multiplicity cell base stations, TOA andTDOA data and timing information to central Location Database Server(LDS). Transmitting location data to interested cellular network clients

[0029] The Location Device Module Functions:

[0030] 1. Receiving succeeding MS Positioning response signal PRS

[0031] 2. Identifying and Decoding incoming PRS signal

[0032] 3. Performing signal identification code (ID) and Time Stampfunctions

[0033] 4. Storing PRS signal delays Δτ in temporary LD memory

[0034] 5. Transmitting packets of collected PRS data from each BS to LDSin forwarding module via digital interface.

[0035] Location Database Server Functions:

[0036] 1. Calculating TDOA location for each MS data from multiplicityof BS and based on applied weighted algorithm for 3-5 BS Location Deviceantennas

[0037] 2. Applying attenuation methods, and angle of arrival methods tosignals from two BS LD antennas

[0038] 3. Optimizing and reducing position ambiguities in case of two ormore available solutions or ambiguious results

BRIEF DESCRIPTION OF THE DRAWINGS

[0039]FIG. 1a: Diagram of Location Device Scheme 1 with additionalsupporting antenna A2 describing Timing Block that is based on the TDOAmeasurements in two reception channels in a single BS.

[0040]FIG. 1b: Diagram of Location Device Scheme 2 with single existingBS antenna A2 describing Timing Block that is based on the TOA method intwo reception channels in two base stations.

[0041]FIG. 1c: Diagram of Location Service Scheme with Location Deviceslocated on each BS. Each LD is synchronized by GPS clock if necessary,processing MSi code signal and calculating TOA and TDOA signal delays: τor Δτ for each MS to be passed to Location Database Server via digitalinterface for MS positioning.

[0042]FIG. 2: Diagram of BS receiver with Timing Block device whichdescribes the time delay phase detector (4) with VC02 oscillator andtiming block LD (6) for phase synchronizing systems from MS VC01oscillator to compensate for the signal phase delay (Time Lag) (3) dueto the signal propagation τ.

[0043]FIG. 3a: Diagram of BS antenna configuration for location of MS inreal time using TOA method. Each BS1 . . . BS5 is synchronized by systemclock and receives MS signal with propagation τ₁, τ₂, . . . τ₅ absolutetime delay.

[0044]FIG. 3b: Diagram of BS antennas A1 . . . A3 configuration withadditional supporting antennas A1, 1 . . . A3, 3 for location of MSusing TDOA and AOA methods showing 3 base stations and their antennaarrangement.

[0045]FIG. 4a: Partial Diagram of Location Device with a RF receiver (2)and IF receiver (3) located in base station BS1 for sequential input toTiming Block Processor for TOA calculations.

[0046]FIG. 4b: Continuation of FIG. 4a

[0047]FIG. 5a: A Partial Diagram for the Timing Block Processor for timedifference measurements TDOA.

[0048]FIG. 5b: Diagram describing signal window frames of severalincoming signals explaining the principles of measurements of timeintervals τ in the Timing Block Processor.

[0049]FIG. 6a: A Partial Diagram of Location Device with a RF receiver(1), antennas A1 and supporting RF receiver (2) and supporting antennaA1, 1 located in base station BS1 for input to sequence correlators andTiming Block Processor for TDOA calculations in this two-antennaconfiguration.

[0050]FIG. 6b: Diagram of 2-Receiver Configuration continued

[0051]FIG. 7: TDOA 3-D Representation

[0052]FIG. 8: Wireless 3D Hyperbolic Trilateral Location Method

[0053]FIG. 9: Single Base Station

[0054]FIG. 10: Two Base Stations

[0055]FIG. 11a: Three Base Stations: AOA Method

[0056]FIG. 11b: Three Base Stations: AT Method

[0057]FIG. 12a: Computations for Case of Three Base Stations

[0058]FIG. 12b: Computations for Case of Three Base Stations (cont.)

[0059]FIG. 13: Four Base Stations

[0060]FIG. 14: Computations for Case of Four Base Stations

DETAILED DESCRIPTION OF THE INVENTION

[0061] In IS-95 CDMA cellular network, each base station BS issynchronized to CDMA system time, which is derived from a precise timereference supplied by GPS satellites. All base stations in CDMA networkuse the same frequency channel, or carrier. Spreading codes are used toseparate all signals in order to assure smooth channelization of bothaccess and traffic communication channels, provide a level of privacyand preventing simple signal despreading. Active BS transmits pilotsignal to MS on the downlink using the same Pseudo-Noise (PN) sequence;however, each pilot is offset in time from the others, allowing thesubscriber to differentiate the signals. Each pilot PN sequence repeatsevery 26.67 ms (at chip rate 1.2288 Mchips/sec). Each BS pilot istransmitted with offset of 64×n-chips (52.08 μs), from other sequences.Every subscriber communicating with the BS uses the same spreading codeand offset (except for propagation delays as will be described later) sothat the long code is used to identify both access and traffic channels.A subscriber unit's (MS) time reference is offset from CDMA system timeby the propagation time delays between base station BS and the mobilesubscriber's phone MS. These propagation delays create time and phaseshifts in the system both in BS-transmitter and MS-receiver oscillators.

[0062] The Cellular Network Operator-initiated Functions

[0063] The Mobile Switching Center MSC is the heart of the wirelessinfrastructure network. Every circuit from a mobile handset MS is servedby BS, which then homes into MSC via the Base Station Controller BSC.The MSC routes the calls to the PSTN, another MSC, an Internet ServiceProvider (ISP) or a private network such as Location Service LS, forconnection to the appropriate destination. To ensure servicecommunications such as LS via traffic management, the wireless networkuses BSC controllers to segment the network and control congestion. Theresult is that MSCs route their circuits to BSCs, which in turn areresponsible for connectivity and routing of calls for 50 to 100 wirelessbase stations BSs. In the present system, the MSC initiates a sequenceof silent Positioning Request Signal (PRS) broadcasts with appropriatelists of BSs, and MSs approximately every 2 seconds via BSC controlchannel to all BSs. The BSs in turn to route the PRS broadcasts to allavailable mobile MSs within that specific mobile cell. The silentPositioning Request Signal (PRS) contain typically each MS code and ID,last recorded cell position in HLR and VLR registers for speedydistribution. Since it is essential to obtain a large number of MSposition signals, the operator must deal with existing communicationtraffic constraints and the need for providing continuous tracking of MSdata.

[0064] The MS responds to position signal PRS only if the MS iscurrently in stand-by (idle) mode. The position service transaction usesreverse control RACCH channel with overall time estimate of about 40 msfor each request/response transaction. (The operator can also obtainpositioning data when MS is engaged, however we will concentrate onstand-by mode MS responses only.) Assuming, that about 1000 channels areavailable at each given BS at any moment the LS capacity can be said tobe about 50 MS/channel/sec. or about 2000 to 2500 MSs per second.

[0065] The Location Device modules LDs, described later in FIGS. 1a and1 b, which are installed on each BS process PRS responses in co-locatedfor Timing Block Time-Start/Stop Stamping, TOA signal delays: τ₁, τ₂, .. . τ_(n), or TDOA Δτ for each MS (FIG. 1c).

[0066] From said multiplicity of cell base stations, TOA and TDOA dataand timing information are then returned to MSC central LocationDatabase Server (LDS) via digital interface. As mentioned before, thePRS positioning broadcast is made periodically say every two seconds inorder to provide continuous anonymous tracking of all available MSs. Inthe interest of protecting privacy of individual MS a unique code coverwill be provided for each MS and the real time tracking data used forstatistical purposes only. Only individual clients interested inspecialized tracking and positioning services may order so from theservice operator after appropriate measures were taken.

[0067] The cellular and PCS/DCs wireless service providers must fullycontrol their own timing references and clocks at MSC locations usingreliable and accurate clocking system that receives timing inputdirectly from GPS. In order to assure accurate data at each LD modulethe LD uses the system synchronization pulse for LD timing.

[0068]FIG. 1c shows a diagram of Location Service Scheme with LocationDevices located on each BS. Each LD shows synchronization by GPS clock,processing of individual MSi code signal and calculating TOA signaldelays τ when using single antenna configuration shown in FIG. 3b. Aswill be shown later, the TOA data from absolute signal time delays aregenerally less reliable for accurate measurements.

[0069] In the preferred embodiment the LD will process TDOA signal timedelay differences on two antennas A1, 1 and A1, 2 shown in FIG. 3a. Allsignal data from each BS will be sent to Location Database Server viadigital interface for MS positioning.

[0070]FIG. 1a shows a partial diagram of Location Device Scheme 1 withadditional supporting antenna A2 describing Timing Block. Thisconfiguration is based on the TDOA method for two-reception channels insingle BS. When only single existing BS antenna A2 is available, FIG.1b: Diagram of Location Device Scheme 2 will apply. The Timing Blockhere is based on the principle of absolute time of arrival TOAdifference measurements in two reception channels in two separate basestations.

[0071]FIG. 2 shows a diagram of phase synchronization between the MSAntenna A1 and the BS heterodyne receiver. This system comprises mobilestation MS with its local oscillator VCO₁ that is synchronized with thebase station BS receiver's: VCO₂ oscillator (2) by means of automaticcontrol device. This device contains phase detector (4), loop filter(7), and gain control (5). Group signal delays result from MS signalpropagation τ and are calculated in Time Lag (3). The processesoccurring in the phase-synchronizing system can be expressed by thedifferential equation:

dφ/dt+Ω _(y) *K(p)*F(φ)=Ω₁  (1)

[0072] where Ω₁ is the initial frequency difference on VC0 ₁ and VC0 ₂,K(p) is the coefficient of filter transfer (7), Ω_(y) the mutualde-tuning, F(φ) the phase detector characteristics (4) (FIG. 2). In thestationary mode under K(p)=1 we obtain from equation (1):

F(φ)=Ω₁/Ω_(y)±2πk  (2)

[0073] where φ=φ₁−φ₂, Ω₁ depends on the time delay between VCO₁ and VCO₂oscillators, i.e., on the value Δφ=ω₀=τ, where ω₀=2τ/T₀ the oscillatorfrequency. It is possible to measure phase shift (time interval τ) witha phasemeter in case of τ/T₀<1. If τ/T₀<1, it is necessary to use ameasuring time device i.e., Timing Block (6), see FIG. 2.

[0074] The group time delay τ of a signal from MS to BS depends on thedistance d=cτ of MS from BS, where c=3*10⁸ m/sec is the speed of lightand is measured in Timing Block (6).

[0075]FIG. 4a shows a partial Diagram of Location Device with a RF Stagereceiver and IF Stage receiver located in BS for communication link witha single MS unit.

[0076] Upon the arrival of MS signal to BS antenna A at high frequencyRF Stage Receiver, the signal is transformed to intermediate frequencyIF. The circuit contains: RF baseband Filters (1) amplifiers (2) mixers(3) synchronized with the frequency of carrier signal in heterodyne (4)in the PLL frequency synthesizer (5) controlled by operator's dedicatedlogical choice code. Synchronized signal conversion is de-modulated indemodulator of IF Stage Receiver. Demodulator contains Mixers (6),Shiffers (7), amplifiers (8) filters of low frequency Filters (9);analog to digital converters (10), frequency divider (4 a) in secondheterodyne of receiver.

[0077] In digital circuits of BS receiver signals go from ADC (10) andenter the decoder of digital M-sequences PN sequencer (23) of PNDescrambler (11), which provides selection of sequences with codeattributes of MS window frames in CDMA.

[0078] Continuing from PN descrambler (11), digital sequences r_(j)I andr_(j)Q from MS signals are passed to correlators (12) and (13)respectively via threshold device (14) and (15), to Correlators (12, 13)and on to Comparator (16). The signal is then returned from lowerfrequency filter (17), amplifier (18) in phase-controlled channel to thePLL synthesizer (5). Digital clock synchronizes base M-sequences forgiven MS. R_(j0) enters the additional correlator (20) through thedecoder (PN Sequence). Output signals from correlators (12) and (20) arelimited by threshold devices (14), (21) responsible for the formation ofshort-pulses and are entered to the time block (19).

[0079] Timing block scheme and signal pulse shapes are shown in FIG. 5aand FIG. 5b respectively.

[0080]FIG. 5b shows Pulses 1 and 2 arriving from thresholds devices (14)and (21) as seen in FIG. 5a and enter into trigger flip-flop (22) wheresamples of square-wave pulses shown in FIG. 5b are produced. Signalduration τ of is proportional to the time delay which appears due topropagation delay on route from MS to BS.

[0081] Square-wave pulses a′ from flip-flop trigger (22) enter intofirst input logic-multiplier device (23 b) and feed pulse packs intosecond logical re-multiplier device (23 b).

[0082] An output signal b′ from device (23 a) in FIG. 5b is formed as aresult of multiplying short-pulses from the oscillator (24), pulsesdetermining measurement time T_(m) from frequency divider (27) f ‘andpulses of overlapping windows of signal frames d’ (FIG. 5b).

[0083] Short-pulse packs in are formed on the multiplier-logic device(23 b) and are fed to the counter (25). The overall number of pulsesreceived in the counter (25) depend on amounts of packs P in one cycleof measurement process T_(m)=N*T_(cr) where N is the frequency divisionfactor, T_(cr)=1/f₂ is the period of repetitions of pulses from theoscillator (24). The measurements of interval timeslot window-frames(FIG. 5b) are in the form of packs of counter pulses c′ (FIG. 5b). Thenumber of pulses in the counter for one time interval is t=τ/T_(cr). Thetotal amount of pulses in the counter equals C=(τ/T_(cr))*P. Theduration of measurement cycle is chosen from the condition T_(m)≦P*T₀where T₀ is the interval of repetitions of idle frames FIG. 5b. Under anappropriate choice of values of T_(cr), N, P, the number in the counter(25) will be proportional to time. In general, measurement times T_(m)are determined by the division factor N in the Divider (27). Informationfrom the counter passes through the decoder (26) and enters the computerCPU. In PDN (Public Digital Network) similar information will be sentfrom other BSs, which are participating in the location of MScalculations.

[0084]FIG. 4a and FIG. 4b show a partial diagram of single MScommunicating with BS. It shows high-frequency RF-Stage Receiver,low-frequency IF-Stage Transmitter and various circuits of multi-channelBS transmitter. Spreading of signal on route from BS to MS contributesto signal delay in the synchronization system. MS signal delay iscorrected in the PLL frequency Synthesizer (5) which also monitors MSsignal frequency and phase delay.

[0085] It is possible to locate MSs by the TOA method if the cellularcommunication system is synchronized and all BSs equipped with the PLLsynthesizers are participating in location measurements. When thiscondition is not present due to mutual frequency and phase delay, theTOA measurements will become inaccurate.

[0086] In non-synchronized cellular communication systems such as GSM(TDMA), we propose to add an additional antenna with communicationchannel on each BS that will be participating in determination oflocation of MSs. The inventive device shown in FIG. 6a and FIG. 6bcontains: two broadband antennas A1, 1 and A1, 2 which are installed onone base station BS1, see also FIG. 3b, one channel in RF Stage Receiver1 with high-frequency circuits for RF1 conversion, and IF Stage Receiver1 for low-frequency conversion, and another channel with RF and IF StageReceivers 2, and Digital Clock (8) in FIG. 6b for signalsynchronization.

[0087] High-frequency circuits for frequency conversion RF1 and RF2contain: Bandwidth filters (1) single-line amplifiers (2), mixers (3),and the general source heterodyne voltages—PLL Frequency Synthesizer(4). Circuits for frequency conversion in IF1 and IF2 in IF Stagereceiver 2 contain: single-line amplifiers, mixers, shifters, divider offrequencies, low-pass filters.

[0088] The digital signal block in FIG. 6b contains analog-to-digitalADC-converters (9), PN Descramler (10), signal-coordinated correlators(11) and (12) (matched filters). The inventive device functions asfollows.

[0089] MS signals enter the two antennas A1, 1 and A1, 2 located on themonitoring BS1. If the MS is located in a distant network cell, theelectromagnetic wave front arrives earlier to antenna A1, 1 than toantenna A1, 2. Their relationship may be described by the right-angledtriangle BCD, from which the time lag may be calculated as

Δτ=(D sin(α))/c=(D cos(β))/c

[0090] where D is the distance between antennas in single BS, α theangle of reception of the electromagnetic wave front, β=90°−α. Phaseshift between signals in antennas is expressed by:

φ=ω₀Δτ=2τf ₀(D/c)cos(β)=(2τD)/λ₀ cos(β)

[0091] where f₀=1/T₀=ω₀/2τ, λ₀=c/f₀ is frequency and duration of carrierwavelength. If the distance between antennas is D<λ₀/2, time lag can bedefined by a phase method. In this case measuring time block may be usedas a phasemeter for measurement limits 0-360°. Under such a smalldistance between dipoles, the antenna functions as a simple arrayantenna. When D>λ₀/2, the phase measurements become ambiguious sinceΔτ>T₀ and φ=2+φ_(iz) CDMA, f=900 Mhz, λ₀32 30 cm, T₀=0.99*10⁻⁸ sec.Ambiguity in the distance measurements is repeated at intervalsd₀=cT₀=2.97 m, d=kd₀+d_(iz), d_(iz)≦cT₀, where φ_(iz), d_(iz) are themeasurements of phase shifts and distance respectively.

[0092] For eliminating ambiguities and improving accuracy of distancemeasurements, we propose to combine TDOA measurements with phasedifference measurements. Signals from antennas A1, 1 and A1, 2 enterinto high-frequency dual-channel RF Stage Receiver in which the signalsare transformed from carrier high-frequencies to the intermediatefrequency f_(pr)=270 Mhz. The software controlled PLL frequencysynthesizer (4) is used as signal from heterodyne receiver. Low IF stagereceiver transforms synchronously high frequency signals into lowfrequencies, and then into digital signals by means of theanalogue-digital converters ADC (9). The signal from frequency divider(6) is used as a heterodyne signal that is then passed through and overto Mixer (3) and to Shiffers (5). Low frequency signals are produced anddivided in mixers (3) and low frequency filters (7). Digital signals aresubdivided by means of decoder (10) by time-coding and id-coding for thegiven MS r_(j) and enter correlators 11 and 12 for first and secondchannels. Short pulses starting from flip-flop trigger (15) are formedby means of treshold devices (13) and (14) and from matched-filtersgenerated responses. Square-wave pulse is an output from trigger (15)and is proportional to propagation wave-delay due to the distance fromMS to BS.

[0093] Duration of pulses is measured by means of pulse-counter from theoscillator (20) as they enter through logical multiplier devices (16)and (17) when input equals logical “1” as received from the window-framemonitor in CDMA (22), trigger (15), frequency divider (24) andoscillator (20) in FIG. 6a. Pulse packets from multiplier-logical device(16) are counted by the counter (23) with the time interruptions.Accuracy of location measurement of MS depends on duration ofmeasurement process T_(m). This time is determined by the pulse durationwith frequency divider (24).

[0094] Signal exchange between BS and MS in the monitoring mode is onDCCH (Digital Control Channel) which provides synchronization offrequency FCCH (Frequency Correction Channel) and SCH (SynchronizationChannel) for time delay compensation.

[0095] Response signal will be sent on the special PCS channel from MSto each BS. Device (22) forms a video-pulse of window-frame interval inthe CDMA PCS channel. It is possible to form similar video-pulse fromdigital signal oscillator (Digital Clock). Measurement duration oftime-interval process T_(m)=N*T_(cr) can be changed by assigningdifferent coefficient factors N by divider (24). The number of pulses,which are accumulated in counter (23) for measurement times T_(m) can becalculated as C=10^(n)*p(Δτ/T_(cr)), hence Δτ=CT_(cr)/(p*10^(n)), wherep represents the amount of time intervals for time T_(m), n is aninteger, and Δτ/T_(cr) is the number of pulses in the measured intervalΔτ. Pulses pass through the decoder (19) and are transmitted to LocationDatabase Server ADS) (4) (FIG. 1a) via digital interface. Similarly,digital information on the values Δτ₁, Δτ₂, . . . , Δτ_(N) received onbase stations BS1, BS2, . . . BSN enters the LDS (4) (FIG. 1a) forcalculation of the MS coordinates. Naturally, additional equipment inexisting BSs will be required for TDOA calculations and therefore it maybe necessary to allocate more time for position requests access calls.An advantage of this method is in improvement of Δt measurements sinceBS receiver's channels are identical with respect to delays.

[0096] It is possible to estimate the azimuth location of an MS by usingarray antennas. If the distance D between antennas A1, 1 and A1, 2 isknown, and the wave phase front WPF direction of lines A1, 1 and A1, 2(FIG. 6a) can be estimated accurately enough, the position of the MS canbe calculated. When the values of D, β and γ are known, the AOA methodcan be applied for calculating the distance from MS to A1, 1 or to A1,2. This method requires improved antenna systems and electronic beamcontrol of receiving electromagnetic waves. The TOA, AOA and TDOAmethods may bring in the following inaccuracies:

[0097] 1. Inaccuracies due to a finite front of pulses formed bythreshold devices, which are determined by the level of receiver noisesand channel interference. The minimum threshold is defined by the signalresolution mp that is calucated as

m _(p) =E/N ₀ =P _(s min)/(P _(nin) B)  (3)

[0098] where E is the energy of bit of information signal, N₀ the energyof noise, B the signal base, P_(s min) the minimum power of signalensuring reliable measurement (sensitivity of receiver −116 db),P_(s min) the noise power of receiver's input. For mobile communicationCDMA systems: P_(s min)=4*10³¹ ¹¹ Bt, P_(nin)=kTF_(n)G=6*10⁻¹⁴ Bt, whereF is the noise bandwidth of receiver 1.5*10⁶ Hz, Gthe receiver's noisecoefficient 7-10 db, B=F/C=130, where F is receiving channel bandwidth(1.25 Mhz), C the rate of information transferral (9.6 Kbit/sec). Fromthe formula (3) we obtain m_(p)=5.12. It follows then that more then 1/5of responses from matched-filter will be impossible to use asresponse-pulses for the trigger (15). If the initial threshold levelfrom filter (15) equals 0.9 from the beginning of the response-pulse,then the duration of pulse is 0.1*t_(b), where t_(b) is the duration ofbit of information signal data. The duration of response pulse can beexpressed as ΔT₁=0.82*10⁻⁷ sec when the repetition frequency ofnoise-image of signal equals 1.238 MHz. After having calculated thevalue m_(p)*B=665.6, it is possible to determine the probability ofcorrect measurement of time interval P_(cm)=0.94 (Skolnic, M. J. RadarHandbook, vol. 1, McGraw-Hill, 1970).

[0099] 2. Errors due to discreteness of measurements of time interval τor Δτ for one cycle that are determined by the period of pulserepetitions from the oscillator (24) in FIG. 5a.

[0100] The error of measurement increases p times as it is proportionalto p measurement repetitions in window-frames in CDMA. This error willbe averaged over the measurement process. The resulting inaccuracy willbe equal to T_(cr){square root}{square root over (p)}=ΔT₂. When thefrequency of oscillator (24) is 100 Mhz, and the number of time lags isp=50, the error will be ΔT₂=7*10³¹ ⁸ sec.

[0101] 3. Errors due to delays in flip-flop trigger (15) (FIG. 6a) whichfor most micro-circuits are approximately ΔT₃ =10 ns. The total error oftime lag measurements will be ΔT_(Σ)=162 ns with probability 0.94. Thiscorresponds to the error ΔT_(Σ)*C=48.6 m in range determination. Signaldelay that appears in standard BS receiver channels can also be measuredand included as systematic equipment delay since it does not vary muchbetween MSs.

[0102] The use of TOA and TDOA methods in the standard TDMA/FDMA systemsbrings about dramatic decrease of accuracy due to narrow bandwidth F=200Khz. Indeed, it is 6 times less precise than measurements achieved inthe standard IS-95 (CDMA) so that in general, the errors may be 300 m ormore. Intelligent mathematical application based on wireless 3Dhyperbolic trilateral location method for determining cell phoneposition and filtering out possible position ambiguities

[0103] Radiolocation systems attempt to locate a MS by measuringpropagation times of the radio signals traveling between the MS and afixed set of BSs. There are three major types of radiolocation systems:those based on signal strength, or attenuation methods (AT), those basedon angle of arrival (AOA), and those measuring time of arrival (TOA orTDOA).

[0104] Typically, signal measurements are used to determine the lengthor direction of paths to/from a MS from/to multiple BSs, and thengeometrical relationships are used to determine the location. The linesof position are the curves that describe the possible location of the MSwith respect to a single BS for each of those methods. Each of the linesof position can be described mathematically using the relative geometryof the BSs and MS, while intersection of those lines indicates thepresumed location of the MS. The same principles could and have beenused to determine locations of cell phones. However, in order to achievegood accuracy in location estimates, it is necessary that line of sightpaths exist between the MS and the BSs that are utilized in the locationprocess, and a minimum of three BSs are available for the purpose. Theseconditions can by no means be always assumed in real situations,especially in urban areas where ambiguities arising from multiplecrossings (multipaths) are very common. Therefore, various combinationsof the above mentioned methods will be used for exhaustive utilizationthe existing data on the one hand, and for filtering out possible falselocations on the other. For convenience, the situations involvingdifferent numbers of available BSs together with appropriate methods orcombinations thereof will be considered one by one starting with thecases of a single BS. The general scheme of computations is shown in theflowchart in FIG. 1. From now on, it will be assumed that coordinates oflocations of all BSs are stored in the database and are available to therelevant algorithms.

[0105] Case of a Single Base Station (Unit 2 in FIG. 8)

[0106] To determine location of MS in this case, a combination of AOAand AT methods may be used as illustrated in FIG. 9. The techniques usedin the AOA method determine the direction of MS relative to the BS,which is a narrow sector between two rays while the AT estimates thedistance, i.e., gives a narrow band between two circles with theircenters at the BS. Their intersection defines a small hatched region inFIG. 2 where the MS is assumed to be located. The resulting locationcannot be considered as very reliable as the data are too scanty toattempt any checkups, and no protection against multipath propagation orsignal distortion could be provided.

[0107] Case of Two Base Stations (Unit 4 in FIG. 8)

[0108] In this case we can use both AOA and AT methods. In general wehave here seven points of intersection for the MS location point (seeFIG. 10):

[0109] A is the point of intersection of the two rays in the AOA method;B₁ and B₂ are two points of intersection of the first ray with twocircular lines corresponding to two BSs in the AT method; B₃ and B₄ aresimilar points for the second ray; and C₁ and C₂ are two points ofintersection of the two circular lines.

[0110] First, we can consider the group of points A, B₁, B₂, B₃, B₄, anddecide whether they are close enough based on some adopted tolerancecriterion. If they are, we can compute the center of the group (byaveraging the coordinates of the points) and take it as a candidate forlocation estimator L₁, otherwise we declare the location undetermined.Second, we can choose the nearest of the two points C₁ and C₂, in FIG.10, it is C₁. Now we can compute the center of the group A, B₁, B₂, B₃,B₄, C₁, and adopt it as the final location estimator L.

[0111] Alternatively, robust methods could be used here as described in‘Redundancy, Ambiguity, and Robust Location Estimators’ below. They havean obvious advantage of being able of producing sensible results even inthe presence of outliers, i.e., gross measurement or other errors.

[0112] Case of Three Base Stations (Unit 6 in FIG. 8)

[0113] In this case, both the AOA and the AT could be used for all threeBSs. The AOA produces three intersections of three pairs of rays i.e.,three candidate points for a location (see FIG. 11a), while the ATproduces six intersections of three pairs of circular lines (see FIG.11b).

[0114] First, we consider the three candidate points produced by AOA. Ifthey are close by our tolerance criterion, we will compute their centerL₁, otherwise they are discarded.

[0115] Similarly, we select three closest points among three pairs inthe AT method (one from each pair), and if they are close enough,compute their center, say L₂. If both L₁ and L₂ have been able to becomputed, the final estimate of location could be compute as theirweighted average

L=α ₁ L ₁ +α ₂ L ₂

[0116] where the weights α₁ and α₂ reflect the degree of our faith inthe reliability of the corresponding estimates. This could be done inmore than one way, in particular, the standard Kalman filter could beexploited here.

[0117] The flow of computation is shown in FIGS. 12a-12 b. In Unit 1,the AOA method computes the three intersections of three pairs of rays.If they are close (Unit 2), the indicator variable AOA is set to 1, andthe center of the group L₂ is computed in Unit 3, otherwise theindicator variable AOA is set to 0 in Unit 4.

[0118] In Unit 5, the AT method computes the six intersections of threepairs of circular lines. If they are close (Unit 6), the indicatorvariable AT is set to 1, and the center of the group L₂ is computed inUnit 7, otherwise the indicator variable AT is set to 0 in Unit 8.

[0119] Now if both indicator variables AOA and AT equal 1 (Units 9 and13), the weight formula above is used for computing the location in Unit16.

[0120] If AOA=0 but AT=1 (Unit 10), the location is set equal to thecenter of group computed by AT method in Unit 11.

[0121] If AOA=1 but AT=0, the location is set equal to the center ofgroup computed by AOA method in Unit 14.

[0122] Finally, if both AOA and AT are zero (Units 9 and 13), nolocation is computed (Unit 12).

[0123] Case of Four Base Stations (Unit 8 in FIG. 8)

[0124] Four base stations will allow using the TDOA method for computing3-dimensional locations of MSs, see FIGS. 7 and 13.

[0125] Location signals emitted by a MS are registered by foursynchronized base station BST dual vibration antennas with their start/stop arrival times. The differential times of arrival of these signalsto BSs can be measured with high precision (e.g. 50 nanoseconds) via GPSclock in the timing block (see above). Using these differential timescollected from four BSs, the application is able to compute3-dimensional location of the MS. This direct method gives explicit (x,y, z) location of the MS and in that differs from existing methods,which rely on approximations.

[0126] To handle ambiguities in case of two or more solutions or/andmultipath effects, it may be necessary to use additional base stations,or other location methods such as Angle of Arrival (AOA) and AttenuationMethod (AT), see below.

[0127]FIG. 13 shows the most general mutual configuration of four BSsand an MS. The paired differences of distances traveled by signals maybe expressed as follows:

MB ₁ −MB ₂ =D ₁₂

MB ₁ −MB ₃ =D ₁₃

MB ₁ −MB ₄ =D ₁₄

[0128] where MB₁ is the distance between the base station B₁ and themoving station M, etc.

[0129] The differences D₁₂ . . . can be written as D₁₂=c*(T₁−T₂), . . .where c is the speed of electromagnetic propagation, T₁ the propagationtime from B₁ to M, etc. Denoting the coordinates of the base stationB_(i) by (x_(i), y_(i), z_(i)) for i=1, 2, 3, 4, and the coordinates ofthe MSM by (x, y, z), these equations can be transformed in thefollowing equations

((x−x ₁)²+(y−y ₁)²+(z−z ₁))^(½)−((x−x ₂)²+(y−y ₂)²+(z−z ₂)²)^(½) =D ₁₂

((x−x ₁)²+(y−y ₁)²+(z−z ₁))^(½)−((x−x ₃)²+(y−y ₃)²+(z−z ₃)²)^(½) =D ₁₃

((x−x ₁)²+(y−y ₁)²+(z−z ₁))^(½)−((x−x ₄)²+(y−y ₄)²+(z−z ₄)²)^(½) =D ₁₄

[0130] These equations can be solved directly in the general case asshown below. Besides, there are a number of particular cases in whichthe computations above can be considerably simplified so that they merita separate consideration (see FIG. 14). These particular cases areidentified by conditions like D₁₂=D₁₃, D₁₂=D₁₃=D₁₄, etc. and will belisted ahead along with the corresponding solutions. We begin though bygiving the direct solution of these equations in the most general case.

x=A+B*z

y=C+D*z

z=(−H±(H ² −G*I)^(½))/G

[0131] (see Redundancy, Ambiguity, and Robust Location Estimatorsbelow).

[0132] Here

A=(b ₁₂₃ *R−d ₁₂₃ *P)/(a ₁₂₃ *P)

B=(b ₁₂₃ *Q−c ₁₂₃ *P)/(a ₁₂₃ *P)

C=−R/P

D=−Q/P

E=(B*(x ₂ −x ₁)+D*(y ₂ −y ₁)+z ₂ −z ₁)/D₁₂

F=0.5*(S ₁ −S ₂ −D ₁₂ ²+2*A*(x ₂ −x ₁)+2*C*(y ₂ −y ₁))/D ₁₂

G=E ² −B ² −D ²−1

H=E*F−B*(A−x ₂)−D*(C−y ₂)+z ₂

I=F ²−(A−x ₂)²−(C−y ₂)² −z ₂ ²

P=−a ₁₂₃ *b ₁₂₄ /a ₁₂₄ +b ₁₂₃

Q=−a ₁₂₃ *c ₁₂₄ /a ₁₂₄ +c ₁₂₃

R=−a ₁₂₃ *d ₁₂₄ /a ₁₂₄ +d ₁₂₃

a ₁₂₃=2*(x ₁ −x ₂)/D ₁₂−2*(x ₁ −x ₃)/D ₁₃

b ₁₂₃=2*(y ₁ −y ₂)/D ₁₂−2*(y ₁ −y ₃)/D ₁₃

c ₁₂₃=2*(z ₁ −z ₂)/D ₁₂−2*(z ₁ −z ₃)/D ₁₃

d ₁₂₃=(S ₂ −S ₁ −D ₁₂ ²)/D ₁₂+(S ₃ +S ₁ +D ₁₃ ²)/D ₁₃

a ₁₂₄=2*(x ₁ −x ₂)/D ₁₂−2*(x ₁ −x ₄)/D ₁₄

b ₁₂₄=2*(y ₁ −y ₂)/D ₁₂−2*(y ₁ −y ₄)/D ₁₄

c ₁₂₄=2*(z ₁ −z ₂)/D ₁₂−2*(z ₁ −z ₄)/D ₁₄

d ₁₂₄=(S ₂ −S ₁ D ₁₂ ²)/D ₁₂+(S ₄ +S ₁ +D ₁₄ ²)/D ₁₃

S ₁ =x ₁ ² +y ₁ ² +z ₁ ²

S ₂ =x ₂ ² +y ₂ ² +z ₂ ²

S ₃ =x ₃ ² +y ₃ ² +z ₃ ²

S ₄ =x ₄ ² +y ₄ ² +z ₄ ²

[0133] Although these formulas are valid in the most general case, weconsider now a number of particular cases in which the computationsabove can be considerably simplified. The conditions under which thosecases are valid make a set of nested condition starting with D₁₂=D₁₃. Wewill be always assuming that equality conditions are listed first, andin a case of D₁₂≠0, D₁₃=0, for example, relabelling should be donefirst.

[0134] All particular cases are obtained by assuming D₁₂=0.

[0135] Case 1: D₁₂=0, D₁₃≠0, D₁₄≠0

[0136] Two subcases will be distinguished here: Case 1.1 and Case 1.2.

[0137] Case 1.1: x_(i)≠x₂ and y₁≠y₂

[0138] In this case, the coordinates of a MS can be computed by theformulas:

x=A+B*z

y=C+D*z

[0139] whereas z is computed as

z=J/G

[0140] or as

z=I/J

[0141] (see Redundancy, Ambiguity, and Robust Location Estimators below)

[0142] Here the symbols A, B, C, etc. have the following values

A=((z ₂ −z ₁ −C*(y ₂ −y ₁))/(x ₂−x₁)

B=½(S ₂ −S ₁)/(x ₂ −x ₁)−D*(y ₂ −y ₁)/(x ₂ −x ₁)

C=(K*(z ₂ −z ₁)−M*(x ₂ −x ₁))/(K*(y ₂ −y ₁)−L*(x ₂ −x ₁))

D=(½K*(S ₂ −S ₁)−N*(x ₂ −x ₁))/(K*(y ₂ −y)−L*(x ₂ −x ₁))

E=(B*(x ₄ x ₁)+D*(y ₄ −y ₁₎₊ z ₄ −z ₁)/D ₄₁

F=0.5*(S ₁ −S ₄ −D ₁₄ ²+2*A*(x ₄ −x ₁)+2*C*(y ₄ −y ₁)/D ₁₄

G=E ² −B ² D ²−1

H=2*(E*F−B*(A−x ₄)−D*(C−y ₄)+z₄)

I=F ²−(A−x ₄)²−(C−y ₄)² −z ₄ ²

J=−H/2−sign(H)*(H ² −G*I)^(½)

K=(x ₁ −x ₃)/D ₁₃−(x ₁ −x ₄)/D ₁₄

L=(y ₁ −y ₃)/D ₁₃−(y ₁ −y ₄)/D ₁₄

M=(z ₁ −z ₃)/D ₁₃−(z ₁ −z ₄)/D ₁₄

N=½(S ₄ −S ₁ −D ₁₄ ²)/D ₁₄−½(S ₃ −S _(1−D) ₁₃ ²)/D ₁₃

[0143] Case 1.2: x₁=x₂ and y₁≠y₂.

[0144] In this case, the coordinates of a MS can be computed by theformulas:

x=A+B*z

y=C+D*z

[0145] whereas z is computed as

z=J/G

[0146] or as

z=I/J

[0147] (see Redundancy, Ambiguity, and Robust Location Estimatorsbelow).

[0148] Here the symbols A, B,C, etc. have the following values:

A=((z ₁ −z ₄)/D ₁₄−(z ₁ − ₃)/D ₁₃−(z ₁ −z ₂)/(y ₂ −y ₁))/K

B=½((S ₄ −S ₁ −D ₁₄ ²)/D ₁₄−(S ₃ −S ₁ −D ₁₃ ²)/D ₁₃ −L*(S ₂ −S ₁)/(y ₂−y ₁))/K

C=(z ₁ −z ₂)/(y ₂ −y ₁)

D=½(S ₂ −S ₁)

E=(B*(x ₄ −x ₁ ₁)+D*(y ₄ −y ₁)+z₄ −z ₁)/D ₁₄

F=0.5*(S ₁ −S ₄ D ₁₄ ²+2*A*(x ₄ −x ₁)+2*C*(y ₄ −y ₁))/D ₁₄

G=E ² −B ² −D ²−1

H=2*(E*F−B*(A−x ₄)−D*(C−y ₄)+z ₄)

I=F ²−(A−x ₄)²−(C−y ₄)² −z ₄ ²

J=−H/2−sign(H)*(H ² −G*I)^(½)

K=(x ₁ −x ₃)/D ₁₃−(x ₁ −x ₄)/D ₁₄

L=(y ₁ −y ₃)/D ₁₃−(y ₁ −y ₄)/D ₁₄

[0149] Case 2: D₁₂ =D ₁₃=0,D₁₄≠0

[0150] In this case, we will also consider two subcases.

[0151] Case 2.1: x₁≠x₃ and y₁≠y₃,x₁≠x₂

[0152] Here x and y are computed by the formulas above

x=A+B*z

y=C+D*z

[0153] whereas z is computed as

z=J/G

[0154] or as

z=I/J

[0155] The symbols A, B, C, etc. have the following values

A=(L*(z ₁ −z ₂)−M*(y ₁ −y ₂))/(L*(x ₂ −x ₁))

B=½(S ₂ −S ₁ −N*(y ₂ −y ₁)/L)/(x ₂ −x ₁)

C=−M/L

D=N/L

E=C*(x ₄ −x ₁)+A*(y ₄ −y ₁)+z₄ −z ₁

F=(D−x ₁)²−(D−x ₄)²+(B−y ₁)²−(B−y ₄)² +z ₁ ² −z ₄ ¹ −D ₁₄ ²

G=C ² +A ² −E ²+1

H=2*(C*(D−x ₄)+A*(B−y ₄)−z ₄)−E*F/D₁₄

I=(D−x ₄)²+(B−y ₄)² +z ₄ ²¼*F ² /D ₁₄ ²

J=−H/2 sign(H)*(H ² <G*I)^(½)

[0156] Case 2.2: x₁=x₃ and y₁≠y₃, x₁≠x₂

[0157] Here x and y are computed by the formulas above

x=A+B*z

y=C+D*z

[0158] whereas z is computed as

z=J/G

[0159] or as

z=I/J

[0160] The symbols A, B, C, etc. have the following values:

A=(z ₁ −z ₃)/(y ₃ y ₁)

B=½(S ₃ −S ₁)/(y ₃ −y ₁)

C=(A*(y ₁ −y ₂)−(z ₂ −z ₁))/(x ₂ −x ₁)

D=(½*(S ₂ −S ₁)B*(y ₂ −y ₁))/(x ₂ −x ₁)

E=C(x ₄ −x ₁)+A*(y ₄ −y ₁)+z ₄ −z ₁

F=(D−x ₁)−(D−x ₄)²+(B−y ₁)²−(B−y ₄)² +z ₄ ² D ₁₄ ²

G=C ² +A ² −E ²+1

H=2*(C*(D−x ₄)+A*(B−y ₄)−z ₄)−E*F/D ₁₄

I=(D−x ₄)²+(B−y ₄)² +z ₄ ²−¼*F ² /D ₁₄ ²

J=−H/2−sign(H)*(H ² −G*I)^(½)

[0161] Case 3: Equirange Configuration

D ₁₂ =D ₁₃ =D ₁₄=0

[0162] In this case, the coordinates of a MS can be computed by theformulas

x=−Δ _(x)/Δ

y=−Δ _(y)/Δ

z=−Δ _(x)/Δ

[0163] where $\Delta_{x} = {{1/2}{\begin{matrix}{S_{1} - S_{2}} & {y_{2} - y_{1}} & {z_{2} - z_{1}} \\{S_{1} - S_{3}} & {y_{3} - y_{1}} & {z_{3} - z_{1}} \\{S_{1} - S_{4}} & {y_{4} - y_{1}} & {z_{4} - z_{1}}\end{matrix}}}$ $\Delta_{y} = {{1/2}{\begin{matrix}{S_{1} - S_{2}} & {x_{2} - x_{1}} & {z_{2} - z_{1}} \\{S_{1} - S_{3}} & {x_{3} - x_{1}} & {z_{3} - z_{1}} \\{S_{1} - S_{4}} & {x_{4} - x_{1}} & {z_{4} - z_{1}}\end{matrix}}}$ $\Delta_{z} = {{1/2}{\begin{matrix}{S_{1} - S_{2}} & {x_{2} - x_{1}} & {y_{2} - y_{1}} \\{S_{1} - S_{3}} & {x_{3} - x_{1}} & {y_{3} - y_{1}} \\{S_{1} - S_{4}} & {x_{4} - x_{1}} & {y_{4} - y_{1}}\end{matrix}}}$ $\Delta = {\begin{matrix}{x_{2} - x_{1}} & {y_{2} - y_{1}} & {z_{2} - z_{1}} \\{x_{3} - x_{1}} & {y_{3} - y_{1}} & {z_{3} - z_{1}} \\{x_{4} - x_{1}} & {y_{4} - y_{1}} & {z_{4} - z_{1}}\end{matrix}}$

[0164] The last determinant Δ is nonzero as the four base stations donot lie on a straight line.

[0165] Redundancy, Ambiguity, and Robust Location Estimators

[0166] The TDOA method described above gives in general two candidatepoints for a MB position in the four base stations case (see formulasfor z above). Other location methods could be used here as well. Thus,the AOA method could be applied for the six paired combinations of basestations producing additional candidate points, and the attenuationmethod would also give a number of feasible locations. The total set ofcandidate locations would have to be sorted out because of presence ofprobable outliers resulting from gross from measurement errors,multipath phenomena, etc. So that redundant candidate points canactually help to improve on location estimators.

[0167] Assume that we obtained a group of points

[0168] (x₁, y₁), (x₂, y₂), . . . (x_(n), y_(n))

[0169] as candidates for the BS position. One feasible estimator of MSlocation is the median of the group. i.e., the point

[0170] M=(x_(M), Y_(M))

[0171] where x_(M) and Y_(M) are computed as medians of thecorresponding coordinates:

x _(M)=median(x ₁ , x ₂ , . . . , x _(n))

y _(M)=median(y ₁ , y ₂ , . . . , y _(n))

[0172] The corresponding unit is Unit 10 in FIG. 8.

[0173] Case of More Than 4 BSs (Unit 9 in FIG. 8)

[0174] In such cases the matters are not much different from the case offour base stations. The TDOA method can be used in conjunction withvarious paired combinations of four bases stations, and other methodscould be applied as well together with computations described in contextof redundancy and ambiguity.

[0175] Refinements and Future Embodiments

[0176] The inventive method and Location Device LD for mobilecommunication systems can be expanded for use in all digitaltechnologies—TDMA, CDMA and GSM. As described herein, any cellularsystem, which is synchronized by, system timing input can be equippedwith fixed location-finding, stand-alone LDs. For unsynchronizednetworks, the signals are also received and Ms position is deducedgeometrically from time delays measured at LD between MS and BS. In ETSITS 101 528 GSM (Version 8.1.0) Location services are enhanced byassistance data broadcast messages from the Serving Mobile LocationCenter (SMLC) and the Mobile Station (MS). In this and previous versionsmany concepts such as Location request broadcasts from SMLC andMS-originating self-position requests are introduced into Phase 2+Digital cellular communications (GSM) system procedures. Similarly, allknown position methods such as TOA, Enhanced Observed Time Difference(E-OTD) and GPS positioning are utilized to deal with particular MSlocation determinations. As described herein, the present inventionprovides a comprehensive approach to location of multiplicity of MSs inorder to accumulate large storage of MS position data in real time forITS evaluations. It is hoped that by optimizing location techniques andtheir traffic loads on existing and future communication networks willadvance and facilitate our goals.

1. Method for simultaneous estimation of locations of a number of mobilestations in a mobile radio communication system that includes a numberof base station cells, a plurality of mobile stations, and a centralprocessing station, the method comprising the steps of: creating “TimingBlock Method” for TOA signal measurements on base stations by usingadditional correlators; using additional correlators in the receiverbase station antennas for TOA measurements in synchronized cell systemson arriving signals on each of said antennas; using additionalsupporting correlator on each base station receiver for timemeasurements of signals between one of said base station antennas and anadditional antenna; and using signal time delays measured in short timeintervals of a few nanoseconds with phase shift measurements withinaccuracy not exceeding 0.5 degrees.
 2. The method of claim 1,comprising using the additional correlators in the receiver BS antennasfor TOA measurements in synchronized cell systems on arriving signalsfor time stop calculations on each of said antennas.
 3. Method asdescribed in claim 1 including forwarding location data and timinginformation obtained from a plurality of base stations.
 4. The method ofclaim 1 comprising: using a server capable of processing in real timethe location and timing data obtained from all base stations andtransforming them into appropriately structured data suitable forstoring in a database and being used in further mathematicalcomputations; storing and updating location and timing data obtainedfrom all base stations relating to a plurality of mobile stations in adatabase; using software to effect calculations of TOA, TDOA,attenuation and other quantities relevant to location of mobilestations; calculating TOA, TDOA, attenuation and other quantitiesrelevant to location of mobile stations, with algorithms that use directand exact methods; and estimating locations of a plurality of mobilestations based on the computed TOA, TDOA, attenuation and other relevantquantities and capable of handling gross measurement errors and positionambiguities resulting from multipath phenomena and other possibleinterference by the use of statistical algorithms.
 5. Method foroperator-initiated continuous location estimation of signals travelingfrom base stations to client mobile stations operating in “idle”stand-by mode and in opposite directions comprising: emitting a positionrequest signal from at least one base station through a control channel;emitting a position signal from each of the mobile stations receivingthe location enquire signal from at least one base station, the locationsignal containing identification information on the corresponding mobilestations; and receiving the position signal from each of the mobilestations in base stations neighboring the corresponding mobile stations.6. Method as described in claim 5 including forwarding location data andtiming information obtained from a plurality of base stations.
 7. Methodof determination of mobile station coordinates by receiving andprocessing of the radio signals from corresponding mobile station inseveral base station located at various distances from each other insingle cell configuration comprising the steps of: measuring signal inbase stations, which also conduct monitoring of the mobile station andexecute synchronization of local oscillator in the mobile station whenit answers a location enquiry signal in one of the base stations;synchronization of the signal frequencies and phasing as realized by GPSclocks on all base station oscillators in a given cell whereas basestation transmission of position signals is in a form of “windowsframes” in a predetermined CDMA standard for all mobile stations;measuring time delays as a time differences between the signal leavingthe supporting correlator and signal arriving on the receiver correlatorlocated in the base station; and transmitting all data to the CentralProcessing Station via standard digital interface.
 8. Method asdescribed in claim 7 including forwarding location data and timinginformation obtained from a plurality of base stations.
 9. Method ofdetermination of mobile station coordinates by utilizing the method oftime difference of arrival (TDOA) of signals by synchronizing signalsfrom two base stations, the method comprising the steps of: utilizing asupporting correlator for receiver and an additional antenna positionedclose to one of said base station antenna receiver whereas theseadditional antennas are collocated at all base station and participatein location service of the mobile stations in a given cell; applying theTDOA method in all of base stations after the monitoring base stationexecutes synchronization of local oscillator in specific mobile stationand it answers the location inquiry signal; applying the TDOA method formeasuring electromagnetic waves between all antennas equipped withsupporting correlators and with the correlators of all receiver basestation antennas; and obtaining time delays as differences of phases insignals received by all antennas.
 10. Method as described in claim 9including forwarding location data and timing information obtained froma plurality of base stations.
 11. Method of communication comprisingtaking measurements of a time interval in case of interruption ofmeasuring process in windows frames in an IS-95 CDMA operating system.12. Method as described in claim 11 including forwarding location dataand timing information obtained from a plurality of base stations. 13.Method of communication comprising taking phase shift measurements incase of the phase interruption of the measuring process of windowsframes in an IS-95 CDMA operating system.
 14. Method as described inclaim 13 including forwarding location data and timing informationobtained from a plurality of base stations.
 15. Apparatus fordetermination of an mobile station location by using base stations basestations operating in a predetermined CDMA standard comprising: atimestamp clock for time delays working with the intervals ofinterruption of window frames in CDMA operating systems; an additionalcontrol communication channel used for receiving location signals fromtwo antennas; a descrambler for keeping the results of time delaymeasurements and transmissions in the PC computer for calculation ofcoordinates of mobile station's using mathematical algorithms describedbelow.
 16. Apparatus as described in claim 15 including means forlocating data and timing information obtained from a plurality of basestations.
 17. Apparatus as described in claim 15, in which the centralprocessing station comprises: server capable of processing in real timethe location and timing data obtained from all base stations andtransforming them into appropriately structured data suitable forstoring in a database and being used in further mathematicalcomputations; database for storing and updating location and timing dataobtained from all base stations relating to a plurality of mobilestations; software for calculating TOA, TDOA, attenuation and otherquantities relevant to location of mobile stations; mathematicalalgorithms calculating TOA, TDOA, attenuation and other quantitiesrelevant to location of mobile stations, that use direct and exact (asopposed to approximations) methods; and statistical algorithms(software) for estimating locations of a plurality of mobile stationsbased on the computed TOA, TDOA, attenuation and other relevantquantities and capable of handling gross measurement errors and positionambiguities resulting from multipath phenomena and other possibleinterference.
 18. Apparatus as described in claim 15 including whereinthe predetermined CDMA standard is the IS-95 CDMA standard.
 19. Centralprocessing station capable of simultaneous estimation of locations of anumber of mobile stations in a mobile radio communication system thatincludes a number of base station cells, a plurality of mobile stations,the central processing station comprising: server capable of processingin real time the location and timing data obtained from all basestations and transforming them into appropriately structured datasuitable for storing in a database and being used in furthermathematical computations; database for storing and updating locationand timing data obtained from all base stations relating to a pluralityof mobile stations; and software for calculating TOA, TDOA, attenuationand other quantities relevant to location of mobile stations, whereinmathematical algorithms are used for calculating TOA, TDOA, attenuationand other quantities relevant to location of mobile stations, that usedirect and exact (as opposed to approximations) methods, and whereinstatistical algorithms are used for estimating locations of a pluralityof mobile stations based on the computed TOA, TDOA, attenuation andother relevant quantities and capable of handling gross measurementerrors and position ambiguities resulting from multipath phenomena andother possible interference.